A long term evolution (LTE) technology is researched and developed based on technology accumulation of super 3G by 3rd Generation Partnership Project (3GPP) for over ten years in order to confront challenges of mobile broadband wireless access (MBWA) technologies such as Worldwide Interoperability for Microwave Access (WiMAX) and the like with the development of mobile communication broadband. The LTE technology has succeeded substantively by the end of 2008 for four years' standardization. An orthogonal frequency division multiplexing (OFDM) is the technical standard to eliminate interferences in cells maximally; however, higher inter-cell interferences (ICI) will happen because the LTE-A technology is still in the same-frequency network, thereby reducing experiences of edge users greatly and limiting the entire capacity of a system largely.
Many technologies, such as power control, flexible spectrum reuse, random interference elimination and the like, are raised and discussed by 3GPP and other organizations to address the issue. These technologies have potential benefit to increase cell-edge user throughput widely, which, however, will cost the whole cell throughput. Accordingly, a coordinated multiple point (CoMP) transmission technology is proposed. The CoMP technology is incorporated into the LTE-A frame in the 54th 3GPP RANI conference in August, 2008. As a promising candidate technology in the LTE-A (LTE-advanced), the CoMP transmission technology plays a role in introducing coordination among base stations and sharing necessary information among the coordinated base stations, thereby inhibiting the ICI effectively, significantly improving the cell-edge user throughput and enhancing the performance of the system. For example, a joint transmission (JT) solution of the CoMP transmission technology is that the coordinated cells serve for one or a plurality of users simultaneously by sharing data information and control information there-among, as shown in FIG. 2. Thus, the interference in each cell can be eliminated and can be transformed into an available signal, thereby greatly improving the cell-edge user performance. However, this solution requires user equipment (UE) to feed back channel information of a plurality of cells and even relative inter-cell channel information so as to ensure joint scheduling, precoding and data transmission implemented by the plurality of cells.
In the LTE-A system, UE estimates channel information from a base station to the UE based on a channel state information reference signal (CSI-RS) configured by the UE, and calculates a channel quality indicator (CQI) and feeds it back thereto, wherein an index of a precoding matrix indicator (PMI) and rank indication (RI, i.e. the number of data streams) may be fed back with the CQI. Thereafter, UE may feed back downlink RI/PMI/CQI in a physical uplink shared channel (PUSCH) in a specific feedback mode after triggering an instruction by downlink control information (DCI) from the base station. Meanwhile, if the cell is configured with a plurality of downlink carrier, it is required to indicate the channel information of the specific carrier to be fed back in the triggered instruction. To obtain channel information of a plurality of transmission points, an upper layer signaling may be used to configure a measurement set for the UE, wherein the measurement set may contain measurement information of the plurality of transmission points, namely, information of a downlink reference signal corresponding to each transmission point. The UE receives the information to measure and feed back downlink channel information of reference signals in the measurement set.
Table 1 illustrates conclusions reached based on triggering of aperiodic CSI feedbacks in R11.
TABLE 12 bit DCITriggered Aperiodic Feedback Sets00no triggered aperiodic CSI feedback01an aperiodic CSI feedback set configured by an upperlayer signaling aiming at a primary carrier10aperiodic CSI feedback set 1 configured by an upperlayer signaling11aperiodic CSI feedback set 2 configured by an upperlayer signaling
Wherein, bits in first DCI is configured to be 00, which represents no triggered aperiodic CSI feedback; bits in the first DCI are configured to be 01, which represents an aperiodic CSI feedback set configured by the upper layer signaling aiming at the primary carrier; bits in the first DCI are configured to be 10, which represents a first aperiodic CSI feedback set configured by the upper layer signaling; and bits in the first DCI are configured to be 11, which represents a second aperiodic CSI feedback set configured by the upper layer signaling.
Additionally, to realize CoMP transmission, only when the UE knows a common reference signal (CRS) configuration of each cell and whether transmission subframes are multicast broadcast single frequency network (MBSFN) subframes, it can correctly demodulate physical downlink shared channels (PDSCH) of all cells served therefor. Because R10 LTE is designed for multiple-input multiple-out-put (MIMO) of a single cell without consideration on CoMP transmission, the UE merely knows CRS configuration and MBSFN sub-frame configuration of a main cell thereof but the related configurations of coordinated cells thereof, so that the UE fails to correctly demodulate the PDSCH when the coordinated cells transmit the PDSCH (JT or DPS) to the UE.
Concerning the issue that how the CoMP UE knows a CRS pattern used by the current PDSCH mapping discussed by 3GPP at present, configuration of a new signalling to notify the UE, namely, CRS pattern DCI (CRS pattern DCI) has been achieved. The solution generally includes support to notify the UE of CRS configuration of one cell and support to notify the UE of CRS configurations of three cells. The specific solution is that candidate CRS pattern sets to support one or three cells are configured in accordance with a radio resource control (RRC) protocol and then the CRS pattern DCI is used to notify the UE of the CRS pattern used by the current PDSCH mapping, so that a user may demodulate the PDSCH correctly. The former has the advantage of lower CRS overhead and the disadvantage of poor flexibility, in which only one cell is required to transmit normal subframes and the remaining cells transmit MBSFN subframes during JT transmission; while the latter can support relatively more JT transmission modes. However, the existing solution still fails to support all the CoMP transmission schemes and can be improved greatly in the flexibility.
A provision of an effective solution is not made aiming at the transmission scheme where poor flexibility and failure to support the CoMP transmission system completely exist in the CRS pattern notification solution in the related arts. Furthermore, communication resources occupied by various signalling in the communication system are valuable, so it is determined that special DCI must be used to trigger the aperiodic CSI feedback in the discussion of the LTE-A standardization, and meanwhile, the issue that how to use the DCI sufficiently is worth being considered in the industry.